The introduction of electronics into weaving technology has been accompanied, from the very beginning, by efforts aimed at removing the causes of jet loom run interruption. One of these causes is an incorrect weft insertion which is detected by a weft stop motion which then gives a signal to stop the machine run. The chief problem in this operation is how to release the incorrectly inserted but already beaten-up weft, especially with fine staple yards.
There are several known mechanisms for this purpose and they can be classified substantially into three groups, viz., mechanisms for drawing out the weft in its axis without releasing it previously, mechanisms releasing the weft by its transverse displacement with subsequent drawing out in the pick axis, and finally mechanisms producing on the incorrectly inserted weft a wave progressing in the pick axis to release the weft progressively and to draw it out then in the pick axis.
The first of these known mechanisms is relatively simple mechanically but not applicable to fine staple yarn wefts due to a high degree of risk of damaging these wefts. A common drawback of the other two mechanisms is their complexity.
There are also several known devices for automatically removing an incorrectly inserted weft. With one of them, the incorrectly inserted, beaten-up and cut off weft is first released by shaft motion, then gripped by manipulator tongs and drawn towards the main jet so as to be presented to the winding device which finishes the removal of the weft from the shed. Another known device for automatic removal of an incorrectly inserted weft operates on a similar principle using its non-separation, and achieving the presentation of the weft to the take down device by means of a portion of the supply of the metering device fed by an ancillary jet. The drawing-off proper is directed towards the main jet, like in the above mentioned known device.
The drawback of the above-mentioned devices is that for releasing the beaten-up weft from the shed, especially with staple yarns, a considerable force is required, in many cases superior to the strength of the weft to be removed. For this reason, the removal of incorrectly inserted wefts by means of such devices is difficult, sometimes even impossible on fine staple yarns. Besides, the devices themselves are considerably complicated and accordingly costly.